Recent Publications

Nonlocal escape of nanoparticles from the negative glow in an acetylene DC discharge: Experiment and PIC modeling

V. Lisovskiy, S. Dudin, S. Bogatyrenko, A. Shakhnazarian, S. Rezunenko

Nanoparticle formation, confinement, and loss in a low-current DC glow discharge in acetylene with vertically oriented electrodes are investigated experimentally and numerically. Laser light scattering reveals the formation of a nanoparticle cloud in the negative glow region at acetylene pressures above 0.15 Torr, whereas no stable cloud is observed at lower pressures. The cloud is localized near the region of maximum plasma emission and evolves in time owing to particle growth and gravity-driven redistribution. A robust nonlocal loss mechanism is observed, whereby nanoparticles leave the confinement region and deposit on the discharge tube walls at positions significantly shifted toward the anode. Transmission electron microscopy demonstrates pronounced spatial size selection, with small nanoparticles confined near the cloud, whereas only large particles and aggregates are transported into the Faraday dark space. Two-dimensional particle-in-cell simulations combined with a force-balance analysis reveal a shallow axial potential pit in the negative glow and a spatially varying near-wall sheath that govern nanoparticle confinement and escape. The calculations show that the smallest nanoparticles carry, on average, less than one elementary charge because of the exceptionally low electron temperature in the negative glow, allowing stochastic charge fluctuations to produce neutral particles that can escape radially to the chamber walls. Larger nanoparticles remain electrostatically confined by the near-wall potential barrier. Because it is localized along the discharge axis, nanoparticles can drift along the confinement boundary toward the anode and bypass the barrier, escaping to the chamber wall. This mechanism provides a physical explanation for the observed nonlocal nanoparticle loss.

Guest editorial: Papers from the 5th International Conference on Data-Driven Plasma Science

Ali Mesbah, Jim Gaffney, Sadruddin Benkadda, Satoshi Hamaguchi

University of California, Inertia, Aix-Marseille University, CNRS, University of Osaka

Multi-petawatt physics at new and future laser user facilities

Jonathan D. Zuegel, Antonino Di Piazza, Karl M. Krushelnick, Daniele Margarone

University of Rochester, University of Michigan, The Extreme Light Infrastructure ERIC

The mini-conference on Multi-Petawatt Physics at New and Future Laser User Facilities, held at the 2024 Annual Meeting of the American Physical Society Division of Plasma Physics, updated worldwide progress at the frontier of multi-petawatt physics, including theoretical, computational, experimental, and technical advances.

On the possibility of low-threshold decay of an obliquely propagating ordinary wave into electron and ion Bernstein waves in ITER ECRH experiments

E. Z. Gusakov, A. Y. Popov

Ioffe Institute

The low-threshold parametric decay of an obliquely propagating ordinary wave into electron and ion Bernstein waves in a plasma with a monotonic density profile is considered. This particular scenario is critical as it provides a mechanism for direct nonlinear energy transfer from the pump beam to both the electron and ion components of the plasma, even under conditions when the ECR absorption is expected by the linear theory to be localized elsewhere. Given its practical significance for future electron cyclotron resonance heating operations on ITER, the results of the analysis are illustrated under ITER-relevant conditions. The parametric decay instability threshold power is shown to be substantially smaller than that of a single gyrotron beam.

FENNECS 3D: A three-dimensional particle-in-cell code for non-neutral plasma dynamics and diocotron instability simulations

P. Giroud-Garampon, J. Loizu, F. Romano, G. Le Bars, J.-P. Hogge

École Polytechnique Fédérale de Lausanne (EPFL)

This work presents the three-dimensional (3D) extension of the FENNECS code, a particle-in-cell framework developed to simulate the dynamics of non-neutral plasmas in complex geometries. The development is motivated by the study of spontaneous electron cloud formation in gyrotron electron guns, which can induce parasitic currents and lead to operational disruptions. The inclusion of 3D effects allows the modeling of the diocotron instability, which plays a major role in limiting the cloud density and driving electron losses. These features are inherently absent from the previous 2D version, where the axisymmetric assumption suppresses all azimuthal dynamics. The 3D capabilities are verified in simplified configurations. Simulations of the diocotron instability in an axially uniform annular electron cloud are found to be in excellent agreement with analytical linear theory. Finite-length effects are also investigated by simulating a cloud confined in a Penning–Malmberg trap, with the code reproducing the expected trends predicted by a linear model. FENNECS 3D is then used to simulate the TRapped Electrons eXperiment, a dedicated setup designed to reproduce the trapping conditions of gyrotron electron guns. Simulations performed under experimentally realistic conditions demonstrate the periodic, self-consistent growth and disruption of the electron cloud due to the diocotron instability. The simulated currents agree quantitatively with experimental measurements in both frequency and amplitude. This work establishes a robust and versatile framework for investigating electron trapping phenomena in gyrotrons and other devices where similar mechanisms are present and represents a significant step forward in the numerical modeling of non-neutral plasmas.

Current action integral for the electrical explosion of tungsten fuzz nanostructure

M. M. Tsventoukh

Lebedev Physical Institute of Russian Academy of Sciences

The following article examines plasma formation via electrical explosion of the tungsten fuzz nanostructure. The electrical resistivity of the helium-filled tungsten nanowire structure obtained in the previous research [Tsventoukh and Kulagin, Phys. Plasmas 31, 092509 (2024)] has been applied to evaluate the specific electrical current action integral and the parameters of arcing explosive cycles. The resistivity was estimated to be ρ1nw(T) = 0.265 mΩ cm × (1 + T/15 kK) for a helium-filled tungsten nanowire and η−2/3 × ρ1nw(T) for a layer of nanowires of relative density η. The electric current action integral for a single helium-filled nanowire h was calculated to be h1nw = 1.2 × 108 A2 cm−4 s and that for the whole nanostructure layer is h = η5/3 × h1nw, which is less than 106 A2 cm−4 s for fuzz layers several μm thick of density η < 1/20. Explosive electron emission (ecton cycle) has been estimated to be in the nanosecond range based on the experimentally measured current density. The average current density during the ecton pulse has been estimated as η2/3/(1 + 2η) × h1nw/(enl) = η2/3/(1 + 2η) × 125 MA cm−2/(l/μm), which depends only on the experimental value of the fuzz burnout depth l (a few μm) and agrees with the experimentally measured values of the average current density. The research showed that an ensemble of “sharp needles,” comprising about 1/10 of the total number of nanowires at the arc crater, can (i) provide a total current approximately equal to the arc current (a few amperes) and (ii) form plasma within tens of picoseconds via explosion by a current density of a few GA/cm2.

Modeling stimulated Brillouin backscatter from the inner laser cones during indirect-drive inertial confinement fusion experiments at the National Ignition Facility

A. J. Kemp, T. Chapman, L. Divol, D. P. Higginson, E. Kur, N. Lemos, S. MacLaren, P. Michel, D. J. Strozzi, G. B. Zimmerman

Lawrence Livermore National Laboratory

We report progress modeling stimulated Brillouin scatter (SBS) at the National Ignition Facility (NIF). For indirect-drive, ignition-relevant hohlraum experiments, backward SBS light is a long-standing concern due to its potential for damaging laser optics as well as affecting the symmetry of the x-ray field that drives capsule implosions. To model SBS, we use maps of underdense plasma conditions, i.e., temperatures, densities, materials, charge states, and flows, from hydrodynamics simulations of the hohlraum to run backscatter simulations with the code pF3D [Berger et al., Phys. Plasmas 26, 012709 (2019)]; the latter calculates propagation of incident- and backscattered light of a NIF quad in the paraxial approximation. For the inner cone quads, in designs that utilize significant wavelength detuning, i.e., those that use cross-beam energy transfer to control implosion symmetry, this approach typically has overestimated both the peak power and the duration of SBS measured in experiments. In this work, we discuss how multi-species hydrodynamics simulations can lead to better agreement with experiments through changes to the simulated plasma conditions and the resulting SBS growth rates. Specifically, we discuss SBS reflectivity in the 23° and 30° inner cone quads, compare simulated spectra to FABS measured ones, and discuss how the time history of the backscattered light is related to the absorption/refraction of the incoming light off density features in the hohlraum plasma.

Machine learning methods to fit interatomic potentials for plasma–surface interactions: A C–H–O–Ar example

Jack S. Draney, Athanassios Z. Panagiotopoulos, David B. Graves

Princeton University

At the core of molecular dynamics (MD) simulations of plasma–surface interactions is the interatomic potential that predicts the energy and forces of atomic configurations. Recently, machine-learned interatomic potentials (MLIPs) have become popular in related fields. These MLIPs, developed for near-equilibrium calculations, are challenged when used for the relatively high-energy, chaotic conditions of plasma–surface interactions. In this paper, active learning is used to produce a large dataset of density functional theory calculations featuring C, H, O, and Ar in configurations relevant to simulations of plasma–surface interactions. These data are then used to train both an MLIP and a classical interatomic potential (reactive force field, ReaxFF) for direct comparison. Both potentials are trained using typical machine learning methods, namely, optimization of a loss function via automatic differentiation with respect to the interatomic potential parameters. Both models performed well on a test dataset, producing comparable errors. However, MD simulations using the MLIP were not consistent with published experiments. In contrast, the trained ReaxFF potential appears to perform well on these tasks. Active learning accompanied by machine-learning-style parameter fitting appears promising as a method for producing transferable interatomic potentials for simulations of plasma–surface interactions.

X-ray diagnostics, analysis, verification, and exploration (xDAVE) code for the prediction and interpretation of x-ray Thomson scattering experiments

Hannah M. Bellenbaum, Dave A. Chapman, Maximilian P. Böhme, Thomas Gawne, Sebastian Schwalbe, Willow M. Martin, Michael Bussmann, Dirk O. Gericke, Uwe Hernandez Acosta, Jan Vorberger, et al.

Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Center for Advanced Systems Understanding (CASUS), Stanford University, Universität Rostock, First Light Fusion Ltd.

X-ray Thomson scattering (XRTS) is a common diagnostic used in the warm dense matter (WDM) regime to estimate plasma parameters like density, temperature, and charge state. Experimental analysis typically relies on a forward model to obtain estimates for these parameters, as the measured spectrum is a convolution of the dynamic structure factor (DSF) and the source-instrument function. The Chihara decomposition, where the spectrum is separated into contributions from bound and free electrons, is commonly used to estimate DSFs in the WDM regime, as it allows for the fast calculation of DSFs and therefore can easily be applied in a large-scale parameter optimization. Due to the limited availability of XRTS codes, we present “x-ray diagnostics, analysis, verification, and exploration”, a code designed to quickly estimate DSFs using the Chihara decomposition and analyze experimental spectra. The code is validated by re-analyzing an experiment with isochorically heated beryllium at the OMEGA Laser Facility. In addition, we demonstrate the applicability of the code to plan experiments and predict scattering spectra through the coupling to a ray-tracing code. Finally, the importance of accounting for the energy-dependence of spectrometer instrument functions is demonstrated by comparing ray-tracing simulations to the standard convolution for strongly compressed beryllium experiments at the National Ignition Facility, similar to previously published results.

Numerical method for dynamic dust charge in molecular dynamics simulations of laboratory and lunar dusty plasma environments

G. A. Holen, R. Mishra, Y. Miyake, W. J. Miloch

University of Oslo, Kobe University

A novel per-time step, per-particle efficient and accurate numerical method for modeling dynamic dust charge in dusty plasma simulations is presented. A variety of charging currents are implemented, and any charging current with an analytical expression or empirical value can be included. While work on charge-varying dust has long existed in the literature, our numerical model provides significant improvements to the spatial and temporal evolution of dust charge for molecular dynamics simulations of dusty plasma. When charge time exceeds simulation time, we allow for non-equilibrium dust charge by coupling the charge convergence to the simulation time step. The model is verified with the well-known Spitzer potential and tested with a simple laboratory RF-plasma discharge background plasma and Particle-In-Cell lunar surface output background plasma. When both gradients in the plasma profiles and gravity are included, the steady state is a dynamic equilibrium, where particles oscillate when using the dynamic dust charge model as opposed to stationary equilibrium for static dust charge. Modeling varying or dynamic dust charge allows exploring new complex dynamics with simulations, such as ion-acoustic waves, dust heating, lunar cavity dust transport, and in general, dynamic equilibrium conditions, which can arise from dynamic dust charge.

Size scaling of acceleration phase energetics and its effects on direct-drive DT-layered implosions

D. Patel, R. Betti, V. Gopalaswamy, A. Lees, D. Cao, R. C. Shah

University of Rochester

A fundamental question in inertial confinement fusion is how implosion performance, and therefore ignition thresholds and fusion gain, evolve with target size. In laser-driven direct drive fusion, the scaling of laser-drive performance with size is critical to this evolution and to extrapolating results from the 30-kJ OMEGA laser-fusion experiments to ignition-class facilities such as the National Ignition Facility. Beyond the well-known adverse effects of cross-beam energy transfer (CBET) on drive performance, here we demonstrate that effects related to the non-scaling physics of thermal conduction and electron–ion energy equilibration exert an influence on drive behavior with scale that equals or surpasses that of CBET. We find that a significant portion of the lost implosion performance with increasing scale is due to the loss of shell implosion velocity. Furthermore, we show that while modest modifications to hydro-scaled designs can recover most of the lost implosion velocity, a full hydro-equivalent performance extrapolation is difficult to achieve without CBET mitigation or subcooling below the triple point of DT.

Effect of static magnetic island on ITG of ADITYA-U tokamak

Vibhor Kumar Singh, Amal R. Biju, Jaya Kumar Alageshan, Kaushlender Singh, Deepti Sharma, Joydeep Ghosh, Nishant Sirse, Abhijit Sen, Sarveshwar Sharma, Manjunatha Valmiki, et al.

Institute for Plasma Research, Indian Institute of Science, Homi Bhabha National Institute, Centre for Development of Advanced Computing, IPS Academy

Magnetic islands play a crucial role in regulating plasma confinement in tokamaks by interacting with micro-instabilities, such as the ion temperature gradient (ITG) mode. This work presents a detailed investigation of the effects of static magnetic islands on ITG instability, relevant to the ADITYA-U tokamak, using the Global Gyrokinetic Code in Cylindrical Coordinates, a particle-in-cell framework that employs a neural-network-assisted projection scheme. A two-phase simulation strategy is adopted. In the first phase, static magnetic islands with mode numbers (m, n) = (2, 1) and (3, 1) are introduced by perturbing the equilibrium magnetic flux functions. Particle dynamics within these modified topologies result in the flattening of plasma density profiles in the island regions, confirming island formation and its impact on the equilibrium profiles. In the second phase, the flattened profiles serve as new equilibria for linear electrostatic gyrokinetic simulations with adiabatic electrons, enabling the study of the modified ITG behavior. Magnetic islands significantly restructure the ITG mode, producing a spatial redistribution of potential fluctuations within and around the island region. Moreover, as the island width increases, the growth rates of different toroidal ITG modes converge, suggesting a universal stabilization trend. A comparison between the (2,1) and (3,1) islands indicates that higher-q islands lead to a more spatially extended ITG mode structure, reflecting the longer magnetic connection lengths and weaker curvature drive at outer flux surfaces. These results demonstrate the pivotal role of island-induced equilibrium modifications in determining ITG stability and mode structure in tokamak plasmas.

Multiscale coupled plasma–feature simulation for 3D profile evolution in Si etching under HBr/Cl2 mixture plasmas

Yeong Geun Yook, Sang Young Chung, Hae Sung You, Jae Hyeong Park, Won Seok Chang, Deuk Chul Kwon, Dong Hun Yu, Byung Jun Lee, Kwang-Ho Kwon, Yeon Ho Im

Korea Institute of Fusion Energy, Jeonbuk National University, Korea University, KWT Solution

Coupling reactor-scale plasma simulations with device-scale three-dimensional (3D) feature evolution models enables predictive profile simulation under realistic plasma boundary conditions. This coupling is essential for accurate analysis and mechanistic interpretation of etched feature evolution during plasma etching processes. However, quantitatively validated multiscale simulations that reliably couple bulk plasma behavior with surface reaction databases for realistic 3D profile prediction remain limited. This study proposes a multiscale simulation framework that integrates reactor-scale plasma predictions with a device-scale 3D profile evolution platform to investigate crystalline Si etching under HBr/Cl2 mixture plasma conditions at varying gas mixing ratios. Reactor-scale simulations predict plasma properties in a virtual sheath regime, providing the characteristics of ion and neutral particles impinging on 3D surfaces. These characteristics are incorporated into a 3D feature profile simulator that computes real-time shape evolution using an effective 3D mesh, Compute Unified Device Architecture-accelerated ballistic transport, and an OpenMP-parallelized surface reaction model. The plasma–surface reaction set estimates etch yields and surface reaction coverages as functions of the HBr/Cl2 mixing ratio and ion energy over a wide range of plasma process conditions. Realistic transport mechanisms include incident ion and neutral distributions from the bulk plasma, reflected ions, and re-emitted neutrals from feature sidewalls. The predicted profile evolution agrees well with the experimental results. Additionally, the model provides quantitative information on the etch rate, ion flux, ion energy, radical fluxes, and reaction coverages, enabling mechanistic interpretation of etching characteristics in HBr/Cl2 mixture plasma etching of crystalline Si.

First-principles closure for anomalous transport in Hall thrusters: Self-consistent implementation and numerical stability

Ioannis G. Mikellides, Alejandro Lopez Ortega

Jet Propulsion Laboratory, California Institute of Technology

This work presents a self-consistent implementation of a first-principles closure model for anomalous electron transport in Hall thrusters, addressing numerical challenges that have thus far hindered incorporation of the authors' previously developed wave-based transport theory. The model, derived from a wave–particle interaction theory in which electron cyclotron drift instability turbulence and its transition to longer-wavelength lower-hybrid modes dominate the nonlinear saturation of the instability, provides both fluid and kinetic formulations for the anomalous momentum-transfer collision frequency and is employed together with the anomalous electron-heating closure previously developed by the authors. When implemented within the generalized Ohm's law, the original formulation leads to a degeneracy in which the electric field vanishes from the current conservation relation, precluding the determination of a unique plasma potential. In this study, a revised scaling of the ion-trapping coefficient combined with a regularization of the azimuthal electron velocity that remains inactive in regions of large drift restore numerically well-posed formulations while preserving the underlying physics of the model. The modified formulation is implemented in a one-dimensional hybrid solver (Hall1De), enabling stable steady-state solutions and systematic numerical investigations. Parametric studies reveal the sensitivity of the anomalous transport profile to key coefficients governing wave growth and saturation, while macroscopic plasma properties remain comparatively insensitive. The results establish a robust framework for embedding physics-based closures in hybrid simulations and provide guidance for further development, including extensions to account for axial ion dynamics and future validation in fully two-dimensional hybrid simulations.

Cascade, cavitation, and mixed regime dynamics in Alfvén ion–acoustic turbulence: A Zakharov approach with applications to the upper solar atmosphere

Garima Patel, Ritu, R. Uma, R. P. Sharma

Indian Institute of Technology Delhi, Delhi Technological University

Turbulence in the upper solar atmosphere and solar wind remains central to the understanding of coronal heating and energy transport. While Langmuir turbulence has been extensively classified into cascade-dominated, cavity-dominated, and mixed regimes, no comparable systematic framework exists for Alfvén turbulence, despite the ubiquity of Alfvénic fluctuations in the upper solar atmosphere. In this work, we extend the classification of turbulence to nondispersive Alfvén waves coupled with ion–acoustic fluctuations using the Zakharov and modified Zakharov systems in one dimension. Both analytical considerations and direct numerical simulations demonstrate that the turbulence character is strongly regulated at fixed amplitude and geometry primarily by the frequency mismatch ΔΩ=ω0−ωk, where ω0 is the driver frequency and ωk is the natural Alfvén wave frequency. ΔΩ serves as the key control parameter for turbulence character at fixed amplitude. For small ΔΩ, modulational instability is strong and cavitation dominates. For large ΔΩ, modulational growth is suppressed, and turbulence becomes cascade-dominated. Intermediate values of ΔΩ produce a mixed regime where cavitation and cascades coexist. This ΔΩ based framework unifies cavitation and cascade processes in Alfvénic systems and provides a possible reduced-model framework relevant to localized coronal heating processes: cavitation mediates localized energy deposition, while parametric decay processes redistribute energy toward larger spatial scales within the model domain.

TRACE: A root-tracking solver for the dominant complex wavenumber of cyclotron waves in warm magnetized plasmas

Yuxuan Wang, Mousen Cheng, Xiaokang Li, Xiong Yang, Wandong Zhao

National University of Defense Technology

Ion cyclotron resonance heating plays a central role in high-power electric propulsion devices such as Variable Specific Impulse Magnetoplasma Rocket, where magnetic beach absorption is the dominant power deposition mechanism. Under magnetic beach conditions, wave damping is primarily collisionless and strongly kinetic in character, rendering cold-plasma models inadequate. Reduced-order kinetic models address this gap by representing the plasma response through the dominant complex root of the kinetic dispersion relation. However, near the ion cyclotron frequency ωci, the dispersion relation admits multiple roots and undergoes a rapid backbend in the complex wavenumber plane, making reliable identification of the dominant root a nontrivial numerical problem. TRACE (Thermal Root-tracking Algorithm for Cyclotron wavEs) is a dispersion solver that resolves this difficulty through root-tracking continuation: starting from the unique, well-behaved Alfvén-branch root at low frequencies, TRACE tracks the dominant root continuously across the resonant frequency range, including conditions of finite oblique propagation, temperature anisotropy, parallel velocity drift, and collisions.

Linear and quasi-linear plasma response to resonant magnetic perturbations during ELM mitigation in HL-3

N. Zhang, Y. Q. Liu, G. Z. Hao, J. M. Yu, T. F. Sun, G. Q. Dong, Yi Liu, L. Wang, J. Huang, M. Y. He, et al.

Southwestern Institute of Physics, General Atomics, Sichuan Technology and Business University, Tsinghua University

Active mitigation of edge-localized modes (ELMs)with the n=1 (n is the toroidal mode number) resonant magnetic perturbation (RMP) has recently been achieved for the first time on the HL-3 tokamak. The linear and quasi-linear plasma responses to RMP fields are numerically investigated by utilizing the MARS-F [Liu et al., Phys. Plasmas 7, 3681 (2000)] and MARS-Q [Liu et al., Phys. Plasmas 20, 042503 (2013)] codes. The linear results show that RMP induces a strong edge-peeling response which facilitates the ELM mitigation. A −50° phase shift for the n=1 coil current between the upper and lower rows of the RMP coils presents the optimal coil phase. MARS-Q quasi-linear results show that: (i) without involving perturbation mode near the plasma edge, the applied RMP has minor side effects on both the toroidal momentum and radial particle transport in this HL-3 case; (ii) allowing weak perturbation mode together with RMP produces finite flow damping and density pump-out level comparable to experiments; and (iii) the modeled flow damping and density pump-out is not very sensitive to the assumed resistivity model (Spitzer vs uniform resistivity). We found that both the neoclassical toroidal viscosity and resonant electromagnetic torques play important roles in the plasma toroidal momentum transport in HL-3.

Electric field-driven Rayleigh–Taylor-like instability in binary complex plasma

Priya Deshwal, Hitendra K. Malik

Indian Institute of Technology Delhi

This study uses two-dimensional molecular dynamics simulations to explore Rayleigh–Taylor-like instability in strongly and weakly coupled binary complex plasmas when heavier dust particles are positioned above the lighter ones, having the same charge-to-mass ratio, in a planar configuration. Langevin dynamics simulations are used to study the evolution of perturbations at the interface between these two distinct species of charged dust particles, subject to an externally applied electric field and an equilibrium charge density gradient. We have performed analytical calculations to determine the growth rate of instability under both strongly and weakly coupled dusty plasma regimes. A striking feature of strongly coupled plasma is that there exists a critical value of wavenumber kc where the growth rate vanishes and above which the growth rate attains negative values, or damping takes place; meaning the perturbations having wavenumber k>kc do not evolve into instability. This critical wave number kc shows a dependence on the electric field, relaxation time, viscosity coefficient, screening parameter, mass density, and charge density of dust particles. Theoretical predictions are subsequently validated through molecular dynamics simulations, enabling the reproduction of the instability in binary complex plasma. In these cases, instability ultimately causes mixing among the charged species. The study comprehensively analyzes the growth rate as a function of various system parameters, and it offers deeper insight into the underlying physical mechanisms.

Global plasma modeling of an air-breathing gridded-ion thruster for very low Earth orbit applications

Charlélie Carer, Solène Verdier, Léo Flack, Adrien Scemama, Federico Petronio

Laboratoire de Physique des Plasmas (LPP), CNRS, Sorbonne Université, École Polytechnique, Institut Polytechnique de Paris

A volume-averaged (zero-dimensional) global model of an atmospheric nitrogen–oxygen mixture is proposed. This model is used to predict the performance of an air-breathing electric gridded-ion thruster. Based on particle and energy balance equations, it computes the densities and temperatures of the different species in the discharge chamber and evaluates the thrust generated by ions extracted from the plasma and accelerated between two grids. Simulation results over a range of input radio frequency (RF) powers and altitudes are used to assess the feasible operating regimes and to identify the main limiting mechanisms. Coupling the global model with a simplified drag analysis indicates that satellite operation should be feasible at altitudes between 200 and 250 km, for RF power levels ranging from 1.5 to 3 kW. However, certain limitations associated with the gas compression system and drag estimation deserve further investigation.

Analytic formula for the interface temperature when a Marshak wave propagates from one medium to the next

Mordecai D. Rosen

Lawrence Livermore National Laboratory

There is current interest in designing and experimentally testing a thin “window” in the gold wall of a laser-heated hohlraum that has produced an igniting capsule. This window can ultimately shine on an external physics package to extend the field of high energy density, taking advantage of the enhanced temperature of the hohlraum following ignition. The window must still have some amount of gold to ensure good drive symmetry for the implosion of the ignition capsule. This thin gold must be backed by a lower-Z material for structural integrity. Simulations of such a two-medium structure show the usual non-linear, x-radiation-driven, conduction-heating Marshak wave (MW) propagating through the thin gold. They also show the MW propagating further through the low-Z backing. The radiation-hydrodynamic simulations show a particular transition temperature at the boundary of the two media. We present here an analytic theory for this value, as a function of the low-Z material, which matches the simulations well. This work may also be of interest to the general problem of transport transitions between two media.